1. Field of Application
The present invention relates to an AC generator for installation in a motor vehicle such as a passenger automobile, truck, etc.
2. Description of Related Art
In general, a voltage regulator apparatus (referred to in the following simply as a voltage regulator) that controls the output from an AC generator of a vehicle, and a rectifier apparatus, are each covered and thereby protected by a housing that is constituted by a rear cover, or rear frame, etc., of the AC generator. Such a voltage regulator includes a cooling fin unit that is attached to the main body of the voltage regulator and is also covered by the housing, where the term “cooling fin unit” is used herein to signify a body that is formed with a plurality of cooling fins. An example of such an AC generator is described in Japanese patent publication No. 2005-12886 (pages 3-6, FIGS. 1-8). With such a type of AC generator, external air which is drawn into the interior of the housing by a fan mounted on the rotor of the AC generator flows between the cooling fins as the AC generator (driven from the vehicle engine) rotates, thereby cooling the fins.
However with such a type of AC generator, when the vehicle engine is running at a low speed, the amount of external air that is driven to flow through the housing that covers the voltage regulator etc., becomes reduced, so that the problem arises that the temperature of the voltage regulator increases during such low-speed operation. In particular, the temperature of the rectifier apparatus will increase due to the reduced level of cooling air flow, and this contributes to increasing the temperature of the voltage regulator. That is to say, the temperature of the voltage regulator may become excessively high due to radiant heat from the rectifier apparatus, i.e., heat produced other than by the voltage regulator itself.
Moreover in recent years, a need has arisen for providing an increased level of output power from a vehicle AC generator when the vehicle engine is running at low speed. Such an increase in output power level tends to increase the temperature within the housing, by increasing the level of radiant heat that affects the voltage regulator, and so increasing the temperature of the voltage regulator during low speed operation.
In order to increase the efficiency of cooling the voltage regulator during such low-speed engine operation and also at other levels of engine speed, it has been proposed in the above-mentioned Japanese patent disclosure to form one or more apertures in the housing, adjacent to the cooling fins, through which external air passes into interior of the AC generator. Part of this cooling air flows between the cooling fins, thereby providing increased efficiency of cooling. Such a configuration is shown for example in FIGS. 4 and 5 of the above-mentioned Japanese patent disclosure, in which the fins 840 of a cooling fin unit 808 are located behind two apertures that are formed in a housing 9, which covers the main body of a voltage regulator 8.
However when this is done in a vehicle that may be subjected to frequent occurrences of water (i.e., spray from the road surface) entering the engine compartment, the problem arises that water may readily be drawn into the interior of the housing that covers the voltage regulator and rectifier apparatus, through such cooling air intake aperture(s). Increased amounts of moisture entering the housing will encourage corrosion of metal parts within the housing interior, and also may cause short-circuits between electrical components. This is a significant problem.